A novel negative photoinitiator-free photosensitive polyimide … · applications allow much simplified and safer processing steps required for obtaining a desired pattern, photosensitive

A novel negative photoinitiator-free photosensitive polyimide

　　　　　Xuesong JIANG Hao Li,Hongyu Wang, Zixing Shi,Jie YIN*

Research Institute of Polymer Materials, School of Chemistry & Chemical

Technology, State Key Laboratory for Composite Materials, Shanghai Jiao Tong

University,Shanghai 200240, People'sRepublic of China

Tel.:＋86-21-54746215; Fax:＋86-21-54747445, E-mail:jyin④sjtu.edu.cn

Abstract:

　　Ａ novel negative photoinitiator-free photosensitive polyimide (PFPS-PI)was

synthesized through introducing the photosensitive 4,4-bis[(4-amino)thiophenyl]

benzophenone (BATPB)into backbone chain and methyl acrylate group into

side-chain of the polyimide, respectively. Photosensitive properties study revealed its

good photolithographic properties, with a resolution about 5μm and ａ sensitivityof

150 mJ/cm^.

Key words:

　　　Photoinitiator-丘ee; Photosensitive; Polyimide

ポリイミド･芳香族系高分子最近の進歩 2007

Introduction

　Polyimides (Pis)are high-performance polymer materials with exceptional thermal

stability and mechanical and electrical properties, which have been widely applied in

the aerospace, electrical, and microelectronics　industries[1皿　Because　their

applications allow much simplified and safer processing steps required for obtaining ａ

desired pattern, photosensitive polyimides (PSPIs)have recently gotten much

attention and played very important roles in the field of semiconductor manufacturing

as protection and insulation layers[8-16]. In the most of photosensitive polyimide

systems, low-molecular weight molecule such as photoinitiators must be needed to

sensitive to UV-light for pattern [^'^].In fact, only a little part of photoinitiators can be

used up in illumination process, resulting in a large amount of photoinitiator residues,

which leads to decrease in thermal, mechanical and electrical properties of photoresist

films[13, 14]. Therefore, photoinitiator-free photosensitive polyimides are highly

desired to overcome this problem｡

　In this text, a photosensitive aromatic diamine 4,4-bis[(4-amino)thiophenyl]

benzophenone (BATPB)was chosen to copolymerize with 4,6-diaminoresocinol

hydrochloric (DAR)and　4,4 -oxydiphthalic　anhydride (ＯＤＰＡ)　to　get

hydoxy-polyimide (PI-OH), which can be further acidylated by methyl acryloyl

chloride　to　obtain　negative　photoinitiator-free　photosensitive　polyimide.　The

photoresist show ａ patterning resolution than 5μm with low 365 nm-UV exposure

dose 450 mJ/cm^.


Experimental Part

Materials

　4,6-diaminoresocinol　dihydrochloric (DAR)and　4,4-bis[(4-amino)thiophenyl]

benzophenone (BATPB)(Synthesized in our lab according to references [19,20])，

4,4'-oxydiphthalic anhydride (OPDA)and Ｙ -valerolactone (from Acros), Methyl

acryloyl chloride (Shanghai Zhixing Chemical Company). Other chemicals are of

analytical grade ｅχceptas noted.

Synthesis of hydroxyl polyimide (PI-OH)

　　DAR (2.13g 0.９ mmol), BATPB (0.501 g 0.1 ｍｍｏｌ)ａｎｄtriethylainine(TEA,

0.208g, 2 mmol)were added to 25ml methyl pyrrolidone (ＮＭＰ)and 8ml toluene

solution. After the mixture was completely dissolved, ODPA (3.10 g，１ mmol), y

-valerolactone (0.2g, ２ mmol )and pyridine(0.16g, ２ mmol)were added to the solution･

Then the miχture was under N2 at 180°C for 5hours. After cooling to the room

temperature, 20 ml NMP was added to the miχture, which was precipitated in

methanol/water (VA^＝1/1). The polymer (PI-OH)was collected by filtrationand dried

in vacuo 80 °C.

Mn＝7.7×10"*(determined using DMF as eluent).Elemental analysis: Calcd. C 64.6, H

2.6, N 6.4, S 1.3. Found C 64.7, H 2.5, N 6.3, S 1.4. 'H NMR ([-d6]DMSO, 400

MHz): 8＝6.63－8.08(5H, aromatic), 10.15 (lH, OH). FT-IR (KBr):3 100-3500(O-H),

1778, 1721, 1376 (imide ring), 1 652cm'＼A｢‾c‾Ar^jjDSC in N2, 20°C/min):285°C;

Td(ＴＧＡｉｎN2, 20°C/min):400°C.


Synthesis ofphotoinitiator-freephotosensitive polyimide (PFPS-PI)

　　An excess amount (2.01g 20 mmol)ｏｆ methyl acryloyl chloride was dissolved in

10 ml NMP, then added dropwise to ａ solution of PI-OH (2.0g)and TEA (2.02g

20mmol)in 20 m1 NMP solution over lh at ov. The mixture was warmed to room

temperature and stirred for 12 h. Then the miχture was filtered to remove triethyl

ammonium chloride and poured into methanol. The precipitate was collected by

filtrationand dried in dried in vacuo 40 °C.

　'H NMR ([-de]DMSO, 400 MHz):5＝6.63-8.08 (5H, aromatic), 5.99-5.95 (2H,

CH2=C)，1.83 (3H, CH3)げＴ-IR(ＫＢr):1778, 1376 (imide ring),1720-1730(imide

ri昭ａｎｄよ仁

),1652(Ａｊ-Ａ｢｣,

2950 (C-H), 1626 cm"'(C＝C).

Tg(DSCinN2,20°C/min):235°C;Td(TGAin N2，20°C/min):300°C.

Anal

　Molecular weights were determined by gelpermeation chromatography (GPC)on a

PerkinElmer Series200 apparatus on the basis of linearpolystyrene(PS)standards.

DMF were used as eluent.

　　'H NMR spectra were recorded on ａ Mercury Plus 400HZ spectrometer with

DMS0-d6 as solvent.

　　FT-m spectrawere recorded on ａPerkin-Elmer Paragon 1000 FTIR spectrometer･

　　UV-vis　spectra　were　recorded　by　Perkin-Elmer　Lambda　20　UV-vis

spectrophotometer.PI was coated on the quartzslide.

　　Elemental analysiswas conducted on an Elementar Varioelapparatus.

　　Differentialscanning calorimetric(DSC)analysis was conducted on ａ Pyris 1


DSC.

　　Themogravimetric analysis (ＴＧＡ)ｗａsrecorded on PerkinElmer TGA-7.

　　The polyimide patterning images were obtained with Profile Measurement

Microscope VF-7500 Series and FEI SIRION 200 scanning electron microscope.

Determination of the photosensitivity

　　The photosensitive PFPS-PI was dissolved in N,N-dimethyl acetamide (ＤＭＡ)ａt

ａ solid content of 1 0 wt%. The films were prepared via spin coating on clean silicon

substrates and prebaked at 80 °C for 2 h. The thickness of films was about 2 μm. The

photoresist films were exposed to a 250W high-pressure mercury lamp with ａ uv

dose of 1.5 mW/cm^. The films were then developed in a miχture of DMA/2-propanol

　　　　　　　　　　　　　　　　　　　　　　　　　卜

(v/v°5/1)for 3min and rinsed with 2-propanol. After development, the films were

dried at 80 °C for 2 h. The weights of the remaining films were plotted against the log

of the exposure dose. The sensitivityand contrast of the photoresists were determined

丘om the plots.

Preparation of/olyimide patterns

　　　The polymer solutions were coated and prebaked with procedure described for

photosensitivity study. The films were exposed in the contact mode with ａ mask for

3min to a 250W high-pressure mercury lamp with a uv dose of 1.5 mW/cml.The

films were then developed in a mixture of DMAﾉ2-propanol (v/v=5/l)for ３ min and

rinsed with 2-propanol. After development, the patterns were dried at 80 °Cfor 2 h and

evaluated with SEM.


Results and Discussions

　　The photosensitive polyimide was synthesized through two processes according to

scheme 1. The PI'ＯＨ was prepared through polycondensation in the presence of the

catalyst systems ofY -valerolactone and pyridine. The molecular weight (Mn)and

polydispersity (Mw/Mn) of PI-OH was determined by GPC as 7.7×10^ and 2.1,

respectively. The structure of polyimide was fully characterized by FT-IR, 'H NMR

(Figure l)and elemental analysis.FT-IR study showed the characteristicabsorption of

imide ring at 1778, 1721 and 1376 cm''. The signal for hydroxyl group appeared in

both 'H NMR (10.14 ppm)and FT-IR (3100-3500 cm"'). These indicate the success

f(:)rswthesis of PI'ＯＨ. The component of PI-OH was determined by elemental

analysis result (sulfur content/nitro content)and･h

NMR (hydroxyl/aromatic ring),

which　showed　ｍ:n　is　about　9:1, similar　to　the　ratio　of reaction　material

(DAR/BATPB). Through acrylation of hydroxyl group in PI-OH, methyl acrylate

group can be easilyintroduced into polyimide side-chain to obtain photoinitiator一free

photosensitive (PFPS-PI). FT-IR and ^H NMR showed no characteristic signal of

hydroxyl group. which indicated that the hydrｏχyi group was almost completely

acrylated.

　　The UV-vis spectra of PI-OH and PFPS-PI are shown in Figure 2(a), from which

we can know that acrylation did not have obvious influence on the UV-vis absorption

of polyimide. The films had ａcutoff wavelength below ４００nm and ａ certain amount

of absorption at 365 run, which should be ascribed to Ｃ＝Ｏ absorption of

photosensitive BATPB ['^].Because the high-pressure mercury lamp delivered ａ uv


light with the strongest emission at 365 nm, absorption at 365 nm can enhance the

photosensitivity for photoresist film [21].Upon the uv light, BAPTB structure in the

polyimide chain can photolysis to produce several kinds of radicals (see Scheme 2),

which can initiate polymerization of methyl acrylate group to form crosslinking

system[22]･Similar to the other photoinitiator containing sulfur group such as

phenylthiobenzophenone　　and　keto-sulfoχide [22. 23]，BAp-pB　has　the　high

photosensitivity, which is very important to photosensitivity ofPFPS-犬PI. To determine

the photolithographic properties of PFPS-PI, thin films about 2μm thickness were

prepared by spin coating on the silicon substrate.The photosensitivity was evaluated

by the irradiation of the films with 365 nm UV-light and by the subsequent

determination of the insoluble fraction after development as a function of ｅχposure

dose (Figure 2(b)). The exposure energy to attainａ0.5 gel fraction(Dg°うis about 150

mJ/cm^, and showed high photosensitivity,which may be due to high photosensitivity

ofBATPB[^'^'^^^｡

　　The patterning images of the PFPS-PI were obtained under ａ uv exposure dose

of 450 mJ/cm^ in ａ contact mode with ａ mask. Figure 3 shows the typical pattern of

the micrographs of PFPS-PI, from which we can know that the resolution is about 5 μ

ｍ.

　　In　　conclusion,　through　　introducing　　the　　photosensitive

4,4-bis[(4-amino)thiophenyl]benzophenone (BATPB)into backbone chain and

methyl acrylate group into side-chain of the polyimide, we synthesized ａ novel

negative photoinitiator-free photosensitive polyimide (PFPS-PI), which has its good


photolithographic properties with a resolution about 5μm and ａ sensitivity of 1 50

mJ/cm^.　Studies will be ongoing　concerning　the effect　of BATPB　amount　in

polyimide chain on the photosensitivity and the influence of acrylation reagent such

as cinnamyl chloride and acryloyl chloride on the electrical and mechanical

properties｡

　　We thanks the Ministry of Science and Technology of China (ＮＯ:

2004AA33H010), Ministry of Education of China (Kuashiji Scholar Project)and the

Science &Technology Commission of Shanghai Municipal Government for their

financialsupport.


　　　　　　　　　　　　　　　　　References

1.　Omote Ｔ.In Polyimide: Fundamentals and Applications; M. K. Ghosh, K. Ｌ｡

　　Mittal, Eds.: Marcel Decker: New York, 1996; Chapter 5: 121-149

2.　Hasegawa M, Hone K. Prog. Polym.Sci. 2001; 26: 259

3. Kim KH, Jang s, Harris FW. Macromolecules 2001; 24: 8952.

4. Watanabe ｙ Shibasaki Y, Ando S, Ueda M. Chem. Mater. 2002; 14: 1726

5. Majita s, Kudo H, Nishikubo TJ. Polym. Sci.: Part Ａ: Polym. Chem. 2004; 42:

　　3697.

6. Sasaki T, Moriuchi H, Yano S. Yokota R. Polymer 2004: 46: 6968.

7. Kulkami M, Kothawade S, Arabale ｑ Wagh D. Polymer 2005; 46: 3369.

8.　Jin xz, Ishii H. J.Appl. Polym. Sci. 2005; 96: 1 6 1 9.

9. Chen H, Yin J. J. Polym. Sci.:PartＡ: Polym. Chem. 2004; 42: 1 735.

10. Seino H, Haba o, Ueda MA. Mochizuki, Polymer 1999; 40: 55 1 ｡

1 1. Chung CM, Cho SY, Kim MS, 0h SY, Moon SY, Optical Mater. 2001; 21: 421.

12. Ueda M, Nakayama Ｔ.Macromolecules 1 996; 29: 6427.

13. Feng K, Tsushima M, Matsumoto T, Kurosaki T. J. Polym. Sci.:Part Ａ: Polｙｍ｡

　　Chem. 1998; 36: 685.

14. Hsu SLC, Fan Ｍ H. Polymer 2004; 45: 1101.

15. Wang YW, Yen CT, Chen we, Polymer 2005; 45: 6959.

16. Hsu SLC, Fan MH. Polymer 2004; 44: 1101.

17. Pyo S, Lee M, Jeon J, Lee J. H,Yi MH, Kim JS, Adv. Funct. Mater. 2005; 15; 619.

18. Moore J. A, Dashe汀AN. Chem. Mater. 1989; 1: 163.


19. Zhang CY, Zhu Ｚχ,Zhu ZK, χｕJP. Chem. J. Chinese Universities 2004; 25: 556.

20. Wang HY, Wei J, Jiang xs, Yin J. Submitted.

2 1 .Fouassier　JP.　　　“Photoinitiation,　Photopolymerization,　and　Photocuring

　　Fundamentals and Applications", Hanser, New York 1995.

22. Allen NS, Corrales T, Edge M, Catalina F, Bianco-Pina Green MA. Polymer 1 998;

　　39: 903.

23. Fouassier JP, Lougnot DJ, Polymer 1995; 36: 5055.


Caption to figures

Figure 1. ^H NMR spectrum of PFPS-PI

Figure 2. (ａ)ＵＶ-Visabsorption spectra of PI-OH and PFPS-PI; (b)Characteristic

UV-exposure curves forPFPS-PI.

Figure 3. Images of photolithographicpatternsfor PFPS-PI (ａ):Opticalphotograph

250×; (b): SEM photograph 1000×.







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A novel negative photoinitiator-free photosensitive polyimide … · applications allow much simplified and safer processing steps required for obtaining a desired pattern, photosensitive